This application relates to an inlet duct for an auxiliary power unit on an airplane.
Auxiliary power units are utilized in aircraft to supply power when the aircraft is not in flight, and in some conditions, during flight. An auxiliary power unit is often provided by a relatively small gas turbine engine, typically located in the tail cone of the aircraft.
When the vent door is open, high levels of noise from the gas turbine engine, and in particular its compression section, are emitted from the inlet duct. This is a particular concern when the aircraft is on the ground with the auxiliary power unit operating.